Medicare Supplement Insurance is a form of private health insurance that helps cover certain Medicare out-of-pocket costs such as deductibles, copayments, and coinsurance.  Over 14 million Americans had a Medicare Supplement Insurance plans in 2018. Medicare Supplement insurance is available to those people age 65 and older enrolled in Medicare Parts A and B and in some states to those under age 65 eligible for Medicare due to disability or End Stage Renal disease. Medicare Supplement insurance plans are not connected with or endorsed by the U.S. government or the federal Medicare program.